CoalCoal is a combustible black or brownish-black sedimentary rock usually
occurring in rock strata in layers or veins called coal beds or coal
seams. The harder forms, such as anthracite coal, can be regarded as
metamorphic rock because of later exposure to elevated temperature and
pressure.
CoalCoal is composed primarily of carbon, along with variable
quantities of other elements, chiefly hydrogen, sulfur, oxygen, and
nitrogen.[1]
CoalCoal is a fossil fuel that forms when dead plant matter
is converted into peat, which in turn is converted into lignite, then
sub-bituminous coal, after that bituminous coal, and lastly
anthracite. This involves biological and geological processes. The
geological processes take place over millions of years.[2]
Throughout human history, coal has been used as an energy resource,
primarily burned for the production of electricity and heat, and is
also used for industrial purposes, such as refining metals.
CoalCoal is
the largest source of energy for the generation of electricity
worldwide, as well as one of the largest worldwide anthropogenic
sources of carbon dioxide releases. The extraction of coal, its use in
energy production and its byproducts are all associated with
environmental and health effects including climate change.[3]
CoalCoal is extracted from the ground by coal mining. Since 1983, the
world's top coal producer has been China.[4] In 2015
ChinaChina produced
3,747 million tonnes of coal – 48% of 7,861 million tonnes world
coal production. In 2015 other large producers were
United StatesUnited States (813
million tonnes),
IndiaIndia (678),
European UnionEuropean Union (539) and Australia
(503).[4] In 2010 the largest exporters were
AustraliaAustralia with 328
million tonnes (27% of world coal export) and
IndonesiaIndonesia with 316
million tonnes (26%),[5] while the largest importers were
JapanJapan with
207 million tonnes (18% of world coal import),
ChinaChina with 195 million
tonnes (17%) and
South KoreaSouth Korea with 126 million tonnes (11%).[6]

Etymology
The word originally took the form col in Old English, from
Proto-GermanicProto-Germanic *kula(n), which in turn is hypothesized to come from
the
Proto-Indo-EuropeanProto-Indo-European root *g(e)u-lo- "live coal".[7] Germanic
cognates include the
Old Frisian kole,
Middle Dutch cole, Dutch kool,
Old High GermanOld High German chol, German Kohle and
Old NorseOld Norse kol, and the Irish
word gual is also a cognate via the Indo-European root.[7] In Old
Turkic languages, kül is "ash(es), cinders", öčür is "quench". The
compound "charcoal" in Turkic is öčür(ülmüş) kül, literally
"quenched ashes, cinders, coals" with elided anlaut ö- and inflection
affixes -ülmüş.[8]
Formation

Example chemical structure of coal

At various times in the geologic past, the Earth had dense forests[9]
in low-lying wetland areas. Due to natural processes such as flooding,
these forests were buried underneath soil. As more and more soil
deposited over them, they were compressed. The temperature also rose
as they sank deeper and deeper. As the process continued the plant
matter was protected from biodegradation and oxidation, usually by mud
or acidic water. This trapped the carbon in immense peat bogs that
were eventually covered and deeply buried by sediments. Under high
pressure and high temperature, dead vegetation was slowly converted to
coal. As coal contains mainly carbon, the conversion of dead
vegetation into coal is called carbonization.[10]
The wide, shallow seas of the
CarboniferousCarboniferous Period provided ideal
conditions for coal formation, although coal is known from most
geological periods. The exception is the coal gap in the
Permian–Triassic extinction event, where coal is rare.
CoalCoal is known
from
PrecambrianPrecambrian strata, which predate land plants—this coal is
presumed to have originated from residues of algae.[11][12]
Ranks

As geological processes apply pressure to dead biotic material over
time, under suitable conditions, its metamorphic grade increases
successively into:

Peat, considered to be a precursor of coal, which has industrial
importance as a fuel in some regions, for example, Ireland and Finland
(In its dehydrated form, peat is a highly effective absorbent for fuel
and oil spills on land and water, and also used as a conditioner for
soil to make it more able to retain and slowly release water.)
Lignite, or brown coal, the lowest rank of coal, used almost
exclusively as fuel for electric power generation

Jet, a compact form of lignite, sometimes polished; used as an
ornamental stone since the Upper Palaeolithic

Sub-bituminous coal, whose properties range between those of lignite
and those of bituminous coal (It is used primarily as fuel for
steam-electric power generation and is also an important source of
light aromatic hydrocarbons for the chemical synthesis industry.)
Bituminous coal, a dense sedimentary rock, usually black, but
sometimes dark brown, often with well-defined bands of bright and dull
material (It is used primarily as fuel in steam-electric power
generation, with substantial quantities used for heat and power
applications in manufacturing and to make coke.)
SteamSteam coal, a grade between bituminous coal and anthracite (It was
once widely used as a fuel for steam locomotives. In this specialized
use, it is sometimes known as "sea coal" in the US.[13] Small steam
coal, also called dry small steam nuts (or DSSN) was used as a fuel
for domestic water heating.)
Anthracite, the highest rank of coal (It is a harder, glossy black
coal used primarily for residential and commercial space heating; it
may be divided further into metamorphically altered bituminous coal
and "petrified oil", as from the deposits in Pennsylvania.)
GraphiteGraphite (It is one of the more difficult coals to ignite and not
commonly used as fuel; it is most used in pencils, or powdered for
lubrication.)

The classification of coal is generally based on the content of
volatiles. However, the exact classification varies between countries.
According to the German classification, coal is classified as
follows:[14]

The middle six grades in the table represent a progressive transition
from the English-language sub-bituminous to bituminous coal. The last
class is an approximate equivalent to anthracite, but more inclusive.
(US anthracite has <6% volatiles.)[vague]
Cannel coalCannel coal (sometimes called "candle coal") is a variety of
fine-grained, high-rank coal with significant hydrogen content. It
consists primarily of "exinite" macerals, now termed "liptinite".
Hilt's law
Main article: Hilt's law
Hilt's law is a geological observation that (within in a small area)
the deeper the coal is found, the higher its rank (or grade). It
applies if the thermal gradient is entirely vertical; however,
metamorphism may cause lateral changes of rank, irrespective of depth.
Content

Chinese coal miners in an illustration of the Tiangong Kaiwu
encyclopedia, published in 1637

The earliest recognized use is from the
ShenyangShenyang area of
ChinaChina 4000 BC
where
NeolithicNeolithic inhabitants had begun carving ornaments from black
lignite.[18]
CoalCoal from the Fushun mine in northeastern
ChinaChina was used
to smelt copper as early as 1000 BC.[19] Marco Polo, the Italian who
traveled to
ChinaChina in the 13th century, described coal as "black
stones ... which burn like logs", and said coal was so plentiful,
people could take three hot baths a week.[20] In Europe, the earliest
reference to the use of coal as fuel is from the geological treatise
On stones (Lap. 16) by the Greek scientist
TheophrastusTheophrastus (c. 371–287
BC):[21][22]

Among the materials that are dug because they are useful, those known
as anthrakes [coals] are made of earth, and, once set on fire, they
burn like charcoal. They are found in Liguria ... and in Elis as
one approaches Olympia by the mountain road; and they are used by
those who work in metals.
— Theophrastus, On Stones (16) translation

OutcropOutcrop coal was used in Britain during the
Bronze AgeBronze Age (3000–2000
BC), where it has been detected as forming part of the composition of
funeral pyres.[23][24] In Roman Britain, with the exception of two
modern fields, "the Romans were exploiting coals in all the major
coalfields in
EnglandEngland and
WalesWales by the end of the second century
AD".[25] Evidence of trade in coal (dated to about AD 200) has been
found at the Roman settlement at Heronbridge, near Chester, and in the
Fenlands of East Anglia, where coal from the Midlands was transported
via the
Car DykeCar Dyke for use in drying grain.[26]
CoalCoal cinders have been
found in the hearths of villas and Roman forts, particularly in
Northumberland, dated to around AD 400. In the west of England,
contemporary writers described the wonder of a permanent brazier of
coal on the altar of
MinervaMinerva at
Aquae SulisAquae Sulis (modern day Bath),
although in fact easily accessible surface coal from what became the
Somerset coalfieldSomerset coalfield was in common use in quite lowly dwellings
locally.[27] Evidence of coal's use for iron-working in the city
during the Roman period has been found.[28] In Eschweiler, Rhineland,
deposits of bituminous coal were used by the Romans for the smelting
of iron ore.[25]

No evidence exists of the product being of great importance in Britain
before the High Middle Ages, after about AD 1000.[29]
MineralMineral coal
came to be referred to as "seacoal" in the 13th century; the wharf
where the material arrived in London was known as Seacoal Lane, so
identified in a charter of King Henry III granted in 1253.[30]
Initially, the name was given because much coal was found on the
shore, having fallen from the exposed coal seams on cliffs above or
washed out of underwater coal outcrops,[29] but by the time of Henry
VIII, it was understood to derive from the way it was carried to
London by sea.[31] In 1257–1259, coal from
Newcastle upon TyneNewcastle upon Tyne was
shipped to London for the smiths and lime-burners building Westminster
Abbey.[29] Seacoal Lane and Newcastle Lane, where coal was unloaded at
wharves along the River Fleet, are still in existence.[32] (See
Industrial processes below for modern uses of the term.)
These easily accessible sources had largely become exhausted (or could
not meet the growing demand) by the 13th century, when underground
extraction by shaft mining or adits was developed.[23] The alternative
name was "pitcoal", because it came from mines. The development of the
Industrial RevolutionIndustrial Revolution led to the large-scale use of coal, as the steam
engine took over from the water wheel. In 1700, five-sixths of the
world's coal was mined in Britain. Britain would have run out of
suitable sites for watermills by the 1830s if coal had not been
available as a source of energy.[33] In 1947, there were some 750,000
miners in Britain,[34] but by 2004, this had shrunk to some 5,000
miners working in around 20 collieries.[35]
Uses today

CoalCoal as fuel
Further information:
ElectricityElectricity generation, Clean coal technology,
Global warming, and List of coal power stations
CoalCoal is primarily used as a solid fuel to produce electricity and heat
through combustion. According to the EIA, world coal consumption is
projected to increase from 2012 to 2040 at an average rate of
0.6%/year, from 153 quadrillion Btu (1 Quad are 36,000,000 tonnes of
coal) in 2012 to 169 quadrillion Btu in 2020, and to 180 quadrillion
Btu in 2040.[36] Efforts around the world to reduce the use of coal
has led some regions to switch to natural gas.
ChinaChina produced 3.47 billion tonnes (3.83 billion short tons) in 2011.
IndiaIndia produced about 578 million tonnes (637.1 million short tons) in
2011. 69% of China's electricity comes from coal. The US consumed
about 13% of the world total in 2010, i.e. 951 million tonnes (1.05
billion short tons), using 93% of it for generation of
electricity.[37] 46% of total power generated in the US was using
coal.[38] The
United StatesUnited StatesEnergyEnergy Information Administration
estimates coal reserves at 7011948000000000000♠948×109 short tons
(860 Gt).[39] One estimate for resources is 18,000 Gt.[40]
When coal is used for electricity generation, it is usually pulverized
and then burned in a furnace with a boiler.[41] The furnace heat
converts boiler water to steam, which is then used to spin turbines
which turn generators and create electricity.[42] The thermodynamic
efficiency of this process has been improved over time; some older
coal-fired power stations have thermal efficiencies in the vicinity of
25%[43] whereas the newest supercritical and "ultra-supercritical"
steam cycle turbines, operating at temperatures over 600 °C and
pressures over 27 MPa (over 3900 psi), can achieve thermal
efficiencies in excess of 45% (LHV basis) using anthracite
fuel,[44][45] or around 43% (LHV basis) even when using lower-grade
lignite fuel.[46] Further thermal efficiency improvements are also
achievable by improved pre-drying (especially relevant with
high-moisture fuel such as lignite or biomass) and cooling
technologies.[47]
An alternative approach of using coal for electricity generation with
improved efficiency is the integrated gasification combined cycle
(IGCC) power plant. Instead of pulverizing the coal and burning it
directly as fuel in the steam-generating boiler, the coal is gasified
(see coal gasification) to create syngas, which is burned in a gas
turbine to produce electricity (just like natural gas is burned in a
turbine). Hot exhaust gases from the turbine are used to raise steam
in a heat recovery steam generator which powers a supplemental steam
turbine. Thermal efficiencies of current IGCC power plants range from
39% to 42%[48] (HHV basis) or ≈42–45% (LHV basis) for bituminous
coal and assuming utilization of mainstream gasification technologies
(Shell, GE Gasifier, CB&I). IGCC power plants outperform
conventional pulverized coal-fueled plants in terms of pollutant
emissions, and allow for relatively easy carbon capture.[citation
needed]
At least 40% of the world's electricity comes from coal,[41][49] and
in 2016, 30% of the United States' electricity came from coal, down
from approximately 49% in 2008.[50][51][52] As of 2012 in the United
States, use of coal to generate electricity was declining, as
plentiful supplies of natural gas obtained by hydraulic fracturing of
tight shale formations became available at low prices.[51]
In Denmark, a net electric efficiency of >47% has been obtained at
the coal-fired Nordjyllandsværket CHP Plant and an overall plant
efficiency of up to 91% with cogeneration of electricity and district
heating.[53] The multifuel-fired Avedøreværket CHP Plant just
outside Copenhagen can achieve a net electric efficiency as high as
49%. The overall plant efficiency with cogeneration of electricity and
district heating can reach as much as 94%.[54]
An alternative form of coal combustion is as coal-water slurry fuel
(CWS), which was developed in the Soviet Union. Other ways to use coal
are combined heat and power cogeneration and an MHD topping cycle.
The total known deposits recoverable by current technologies,
including highly polluting, low-energy content types of coal (i.e.,
lignite, bituminous), is sufficient for many years.[quantify]
Consumption is increasing and maximal production could be reached
within decades (see world coal reserves, below). On the other hand,
much may have to be left in the ground to avoid climate
change.[55][56]
Switch to natural gas
Worldwide natural gas generated power has increased from 740 TW in
1973 to 5140 TW in 2014, generating 22% of the worlds total
electricity, approximately half as much as generated with coal.[57] In
addition to generating electricity, natural gas is also popular in
some countries for heating and as an automotive fuel.
The use of coal in the
United KingdomUnited Kingdom declined as a result of the
development of
North Sea oilNorth Sea oil and the subsequent
Dash for GasDash for Gas from the
1990s to 2000.
In
CanadaCanada some coal power plants such as the Hearn Generating Station
have stopped burning coal by switching the plant to natural gas.
In the United States, 27 gigawatts of capacity from coal-fired
generators was slated to be retired from 175 US coal-fired power
plants between 2012 and 2016.[58]
Natural gasNatural gas showed a corresponding
jump, increasing by a third over 2011.[59] Coal's share of US
electricity generation dropped to just over 36%.[59] Due to emergence
of shale gas, coal consumption declined from 2009.[60] Natural gas
accounted for 81% of new power generation in the US between 2000 and
2010.[61] Coal-fired generation puts out about twice the amount of
carbon dioxide—around 2,000 pounds for every megawatt hour
generated—than electricity generated by burning natural gas at 1,100
pounds of greenhouse gas per megawatt hour. As the fuel mix in the
United StatesUnited States has changed to reduce coal and increase natural gas
generation, carbon dioxide emissions have unexpectedly fallen. Those
measured in the first quarter of 2012 were the lowest of any recorded
for the first quarter of any year since 1992.[62]
Coking coal and use of coke
Main article: Coke (fuel)

Coke oven at a smokeless fuel plant in Wales, United Kingdom

Coke is a solid carbonaceous residue derived from coking coal (a
low-ash, low-sulfur bituminous coal, also known as metallurgical
coal), which is used in manufacturing steel and other iron
products.[63] Coke is made from coking coal by baking in an oven
without oxygen at temperatures as high as 1,000 °C
(1,832 °F), driving off the volatile constituents and fusing
together the fixed carbon and residual ash. Metallurgical coke is used
as a fuel and as a reducing agent in smelting iron ore in a blast
furnace.[64] The result is pig iron, and is too rich in dissolved
carbon, so it must be treated further to make steel.
Coking coal should be low in ash, sulfur, and phosphorus, so that
these do not migrate to the metal.[63] Based on the ash percentage,
the coking coal can be divided into various grades. These grades are:

The coke must be strong enough to resist the weight of overburden in
the blast furnace, which is why coking coal is so important in making
steel using the conventional route. However, the alternative route is
direct reduced iron, where any carbonaceous fuel can be used to make
sponge or pelletised iron. Coke from coal is grey, hard, and porous
and has a heating value of 24.8 million Btu/ton (29.6 MJ/kg). Some
cokemaking processes produce valuable byproducts, including coal tar,
ammonia, light oils, and coal gas.
Petroleum cokePetroleum coke is the solid residue obtained in oil refining, which
resembles coke, but contains too many impurities to be useful in
metallurgical applications.
Gasification
Main articles:
Coal gasificationCoal gasification and Underground coal gasification
Coal gasificationCoal gasification can be used to produce syngas, a mixture of carbon
monoxide (CO) and hydrogen (H2) gas. Often syngas is used to fire gas
turbines to produce electricity, but the versatility of syngas also
allows it to be converted into transportation fuels, such as gasoline
and diesel, through the Fischer-Tropsch process; alternatively, syngas
can be converted into methanol, which can be blended into fuel
directly or converted to gasoline via the methanol to gasoline
process.[66]
GasificationGasification combined with Fischer-Tropsch technology is
currently used by the
SasolSasol chemical company of
South AfricaSouth Africa to make
motor vehicle fuels from coal and natural gas. Alternatively, the
hydrogen obtained from gasification can be used for various purposes,
such as powering a hydrogen economy, making ammonia, or upgrading
fossil fuels.
During gasification, the coal is mixed with oxygen and steam while
also being heated and pressurized. During the reaction, oxygen and
water molecules oxidize the coal into carbon monoxide (CO), while also
releasing hydrogen gas (H2). This process has been conducted in both
underground coal mines and in the production of town gas which was
piped to customers to burn for illumination, heating, and cooking.

C (as Coal) + O2 + H2O → H2 + CO

If the refiner wants to produce gasoline, the syngas is collected at
this state and routed into a Fischer-Tropsch reaction. If hydrogen is
the desired end-product, however, the syngas is fed into the water gas
shift reaction, where more hydrogen is liberated.

CO + H2O → CO2 + H2

Liquefaction
Main article:
CoalCoal liquefaction
CoalCoal can also be converted into synthetic fuels equivalent to gasoline
or diesel by several different direct processes (which do not
intrinsically require gasification or indirect conversion).[67] In the
direct liquefaction processes, the coal is either hydrogenated or
carbonized.
HydrogenationHydrogenation processes are the Bergius process,[68] the
SRC-I and SRC-II (Solvent Refined Coal) processes, the NUS Corporation
hydrogenation process[69][70] and several other single-stage and
two-stage processes.[71] In the process of low-temperature
carbonization, coal is coked at temperatures between 360 and
750 °C (680 and 1,380 °F). These temperatures optimize the
production of coal tars richer in lighter hydrocarbons than normal
coal tar. The coal tar is then further processed into fuels. An
overview of coal liquefaction and its future potential is
available.[72]
Coal liquefactionCoal liquefaction methods involve carbon dioxide (CO2) emissions in
the conversion process. If coal liquefaction is done without employing
either carbon capture and storage (CCS) technologies or biomass
blending, the result is lifecycle greenhouse gas footprints that are
generally greater than those released in the extraction and refinement
of liquid fuel production from crude oil. If CCS technologies are
employed, reductions of 5–12% can be achieved in
CoalCoal to Liquid
(CTL) plants and up to a 75% reduction is achievable when co-gasifying
coal with commercially demonstrated levels of biomass (30% biomass by
weight) in coal/biomass-to-liquids plants.[73] For future synthetic
fuel projects, carbon dioxide sequestration is proposed to avoid
releasing CO2 into the atmosphere. Sequestration adds to the cost of
production.
Refined coal
Main article: Refined coal

Traditional works of coal. Valencian Museum of Ethnology.

Refined coal is the product of a coal-upgrading technology that
removes moisture and certain pollutants from lower-rank coals such as
sub-bituminous and lignite (brown) coals. It is one form of several
precombustion treatments and processes for coal that alter coal's
characteristics before it is burned. The goals of precombustion coal
technologies are to increase efficiency and reduce emissions when the
coal is burned. Depending on the situation, precombustion technology
can be used in place of or as a supplement to postcombustion
technologies to control emissions from coal-fueled boilers.
Industrial processes
Finely ground bituminous coal, known in this application as sea coal,
is a constituent of foundry sand. While the molten metal is in the
mould, the coal burns slowly, releasing reducing gases at pressure,
and so preventing the metal from penetrating the pores of the sand. It
is also contained in 'mould wash', a paste or liquid with the same
function applied to the mould before casting.[74] Sea coal can be
mixed with the clay lining (the "bod") used for the bottom of a cupola
furnace. When heated, the coal decomposes and the bod becomes slightly
friable, easing the process of breaking open holes for tapping the
molten metal.[75]
Production of chemicals

Production of chemicals from coal

CoalCoal is an important feedstock in production of a wide range of
chemical fertilizers and other chemical products.[76] The main route
to these products is coal gasification to produce syngas. Primary
chemicals that are produced directly from the syngas include methanol,
hydrogen and carbon monoxide, which are the chemical building blocks
from which a whole spectrum of derivative chemicals are manufactured,
including olefins, acetic acid, formaldehyde, ammonia, urea and
others. The versatility of syngas as a precursor to primary chemicals
and high-value derivative products provides the option of using
relatively inexpensive coal to produce a wide range of valuable
commodities.
Historically, production of chemicals from coal has been used since
the 1950s and has become established in the market. According to the
2010 Worldwide
GasificationGasification Database,[77] a survey of current and
planned gasifiers, from 2004 to 2007 chemical production increased its
gasification product share from 37% to 45%. From 2008 to 2010, 22% of
new gasifier additions were to be for chemical production.
Because the slate of chemical products that can be made via coal
gasification can in general also use feedstocks derived from natural
gas and petroleum, the chemical industry tends to use whatever
feedstocks are most cost-effective. Therefore, interest in using coal
tends to increase for higher oil and natural gas prices and during
periods of high global economic growth that may strain oil and gas
production. Also, production of chemicals from coal is of much higher
interest in countries like South Africa, China,
IndiaIndia and the United
States where there are abundant coal resources. The abundance of coal
combined with lack of natural gas resources in
ChinaChina is strong
inducement for the coal to chemicals industry pursued there. In the
United States, the best example of the industry is Eastman Chemical
Company which has been successfully operating a coal-to-chemicals
plant at its Kingsport, Tennessee, site since 1983. Similarly, Sasol
has built and operated coal-to-chemicals facilities in South Africa.
CoalCoal to chemical processes do require substantial quantities of water.
As of 2013 much of the coal to chemical production was in the People's
Republic of China[78][79] where environmental regulation and water
management[80] was weak.[81]
CoalCoal industry
Main pages: Category:
CoalCoal companies,
CoalCoal mining,
CoalCoal industry in
China,
CoalCoal industry in Pakistan,
CoalCoal industry in India, Coal
industry in New Zealand, and
CoalCoal companies of Australia
See also:
Coal Industry Nationalisation Act 1946 and
CoalCoal Industry
Commission Act 1919
CoalCoal as a traded commodity
In North America, Central Appalachian coal futures contracts are
currently traded on the
New York Mercantile ExchangeNew York Mercantile Exchange (trading symbol
QL). The trading unit is 1,550 short tons (1,410 t) per contract,
and is quoted in U.S. dollars and cents per ton. Since coal is the
principal fuel for generating electricity in the United States, coal
futures contracts provide coal producers and the electric power
industry an important tool for hedging and risk management.[82]
In addition to the NYMEX contract, the
Intercontinental ExchangeIntercontinental Exchange (ICE)
has European (Rotterdam) and South African (Richards Bay) coal futures
available for trading. The trading unit for these contracts is 5,000
tonnes (5,500 short tons), and are also quoted in U.S. dollars and
cents per ton.[83]
The price of coal increased from around $30.00 per short ton in 2000
to around $150.00 per short ton as of September 2008. As of October
2008, the price per short ton had declined to $111.50. Prices further
declined to $71.25 as of October 2010.[84] In early 2015, it was
trading near $56/ton.[85]
Environmental and health effects
Main article: Environmental impact of the coal industry

Health effects
The use of coal as fuel causes adverse health impacts and deaths.[86]
The deadly London smog was caused primarily by the heavy use of coal.
In the
United StatesUnited States coal-fired power plants were estimated in 2004 to
cause nearly 24,000 premature deaths every year, including 2,800 from
lung cancer.[87] Annual health costs in Europe from use of coal to
generate electricity are €42.8 billion, or $55 billion.[88] Yet the
disease and mortality burden of coal use today falls most heavily upon
China.[89][90][91]
Breathing in coal dust causes coalworker's pneumoconiosis which is
known colloquially as "black lung", so-called because the coal dust
literally turns the lungs black from their usual pink color.[92] In
the
United StatesUnited States alone, it is estimated that 1,500 former employees
of the coal industry die every year from the effects of breathing in
coal mine dust.[93]
Around 10% of coal is ash,[94]
Coal ashCoal ash is hazardous and toxic to
human beings and other living things.[95]
Coal ashCoal ash contains the
radioactive elements uranium and thorium.
Coal ashCoal ash and other solid
combustion byproducts are stored locally and escape in various ways
that expose those living near coal plants to radiation and
environmental toxics.[96]
Huge amounts of coal ash and other waste is produced annually. In
2013, the US alone consumed on the order of 983 million short tonnes
of coal per year.[97] Use of coal on this scale generates hundreds of
millions of tons of ash and other waste products every year. These
include fly ash, bottom ash, and flue-gas desulfurization sludge, that
contain mercury, uranium, thorium, arsenic, and other heavy metals,
along with non-metals such as selenium.[98]
The American Lung Association, the American Nurses' Association, and
the
Physicians for Social Responsibility released a report in 2009
which details in depth the detrimental impact of the coal industry on
human health, including workers in the mines and individuals living in
communities near plants burning coal as a power source. This report
provides medical information regarding damage to the lungs, heart, and
nervous system of Americans caused by the burning of coal as fuel. It
details how the air pollution caused by the plume of coal smokestack
emissions is a cause of asthma, strokes, reduced intelligence, artery
blockages, heart attacks, congestive heart failure, cardiac
arrhythmias, mercury poisoning, arterial occlusion, and lung
cancer.[3]
More recently, the Chicago School of Public Health released a largely
similar report, echoing many of the same findings.[99]
Though coal burning has increasingly been supplanted by less-toxic
natural gas use in recent years, a 2010 study by the Clean Air Task
Force still estimated that "air pollution from coal-fired power plants
accounts for more than 13,000 premature deaths, 20,000 heart attacks,
and 1.6 million lost workdays in the U.S. each year." The total
monetary cost of these health impacts is over $100 billion
annually.[100]
A 2017 study in the Economic Journal found that for Britain during the
period 1851–1860, "a one standard deviation increase in coal use
raised infant mortality by 6–8% and that industrial coal use
explains roughly one-third of the urban mortality penalty observed
during this period."[101]
Environmental effects
Coal miningCoal mining and coal fueling of power station and industrial processes
can cause major environmental damage.[102]
Water systems are affected by coal mining.[103] For example, mining
affects groundwater and water table levels and acidity. Spills of fly
ash, such as the
Kingston Fossil PlantKingston Fossil Plant coal fly ash slurry spill, can
also contaminate land and waterways, and destroy homes. Power stations
that burn coal also consume large quantities of water. This can affect
the flows of rivers, and has consequential impacts on other land uses.
One of the earliest known impacts of coal on the water cycle was acid
rain. Approximately 75 Tg/S per year of sulfur dioxide (SO2) is
released from burning coal. After release, the sulfur dioxide is
oxidized to gaseous H2SO2 which scatters solar radiation, hence its
increase in the atmosphere exerts a cooling effect on climate. This
beneficially masks some of the warming caused by increased greenhouse
gases. However, the sulfur is precipitated out of the atmosphere as
acid rain in a matter of weeks,[104] whereas carbon dioxide remains in
the atmosphere for hundreds of years. Release of SO2 also contributes
to the widespread acidification of ecosystems.[105]
Disused coal mines can also cause issues. Subsidence can occur above
tunnels, causing damage to infrastructure or cropland.
Coal miningCoal mining can
also cause long lasting fires, and it has been estimated that
thousands of coal seam fires are burning at any given time.[106] For
example, there is a coal seam fire in
GermanyGermany that has been burning
since 1668, and is still burning in the 21st century.[107]
Some environmental impacts are modest, such as dust nuisance. However,
perhaps the largest and most long term effect of coal use is the
release of carbon dioxide, a greenhouse gas that causes climate change
and global warming, according to the IPCC and the EPA.
CoalCoal is the
largest contributor to the human-made increase of CO2 in the
atmosphere.[108]
The production of coke from coal produces ammonia, coal tar, and
gaseous compounds as by-products which if discharged to land, air or
waterways can act as environmental pollutants.[109] The Whyalla
steelworks is one example of a coke producing facility where liquid
ammonia is discharged to the marine environment.
In 1999, world gross carbon dioxide emissions from coal usage were
8,666 million tonnes of carbon dioxide.[110] In 2011, world gross
emissions from coal usage were 14,416 million tonnes.[111] For every
megawatt-hour generated, coal-fired electric power generation emits
around 2,000 pounds of carbon dioxide, which is almost double the
approximately 1100 pounds of carbon dioxide released by a natural
gas-fired electric plant.[112] Because of this higher carbon
efficiency of natural gas generation, as the market in the United
States has changed to reduce coal and increase natural gas generation,
carbon dioxide emissions may have fallen.[113] Those measured in the
first quarter of 2012 were the lowest of any recorded for the first
quarter of any year since 1992.[114] In 2013, the head of the UN
climate agency advised that most of the world's coal reserves should
be left in the ground to avoid catastrophic global warming.[115]
Clean coal technology
Main article: Clean coal technology
"Clean" coal technology is a collection of technologies being
developed to mitigate the environmental impact of coal energy
generation.[116] Those technologies are being developed to remove or
reduce pollutant emissions to the atmosphere. Some of the techniques
that would be used to accomplish this include chemically washing
minerals and impurities from the coal, gasification (see also IGCC),
improved technology for treating flue gases to remove pollutants to
increasingly stringent levels and at higher efficiency, carbon capture
and storage technologies to capture the carbon dioxide from the flue
gas and dewatering lower rank coals (brown coals) to improve the
calorific value, and thus the efficiency of the conversion into
electricity. Figures from the
United StatesUnited States Environmental Protection
Agency show that these technologies have made today's coal-based
generating fleet 77 percent cleaner on the basis of regulated
emissions per unit of energy produced.[117]
Clean coal technologyClean coal technology usually addresses atmospheric problems resulting
from burning coal. Historically, the primary focus was on SO2 and NOx,
the most important gases in causation of acid rain, and particulates
which cause visible air pollution and deleterious effects on human
health. More recent focus has been on carbon dioxide (due to its
impact on global warming)[118] and concern over toxic species such as
mercury.[119] Concerns exist regarding the economic viability of these
technologies and the timeframe of delivery,[120] potentially high
hidden economic costs in terms of social and environmental
damage,[121] and the costs and viability of disposing of removed
carbon and other toxic matter.[122][123]

An oxyfuel CCS power plant operation processes the exhaust gases so as
to separate the CO2 so that it may be stored or sequestered

Several different technological methods are available for the purpose
of carbon capture as demanded by the clean coal concept:

Pre-combustion capture – This involves gasification of a feedstock
(such as coal) to form synthesis gas, which may be shifted to produce
a H2 and CO2-rich gas mixture, from which the CO2 can be efficiently
captured and separated, transported, and ultimately sequestered,[124]
This technology is usually associated with Integrated Gasification
Combined Cycle process configurations.[125]
Post-combustion capture – This refers to capture of CO2 from exhaust
gases of combustion processes, typically using sorbents, solvents, or
membrane separations to remove CO2 from the bulk gases.[126]
Oxy-fuel combustionOxy-fuel combustion – Fossil fuels such as coal are burned in a
mixture of recirculated flue gas and oxygen, rather than in air, which
largely eliminates nitrogen from the flue gas enabling efficient,
low-cost CO2 capture.[127]

The Kemper County IGCC Project, a 582 MW coal gasification-based power
plant, will use pre-combustion capture of CO2 to capture 65% of the
CO2 the plant produces, which will be utilized/geologically
sequestered in enhanced oil recovery operations.[128] If the
technology used at the
Kemper ProjectKemper Project is successful, it will be the
United States’ first clean coal plant.[129]
The Saskatchewan Government's
Boundary Dam Power StationBoundary Dam Power Station Integrated
CarbonCarbon Capture and Sequestration Demonstration Project will use
post-combustion, amine-based scrubber technology to capture 90% of the
CO2 emitted by Unit 3 of the power plant; this CO2 will be pipelined
to and utilized for enhanced oil recovery in the Weyburn oil
fields.[130] However, only about a half of this CO2 will actually be
permanently stored, the remainder is released into the atmosphere
during capturing, and the processing in the oil field.[131]
An early example of a coal-based plant using (oxy-fuel) carbon-capture
technology is Swedish company Vattenfall's Schwarze Pumpe power
station located in Spremberg, Germany, built by German firm Siemens,
which went on-line in September 2008.[132][133] The facility captures
CO2 and acid rain producing pollutants, separates them, and compresses
the CO2 into a liquid. Plans are to inject the CO2 into depleted
natural gas fields or other geological formations.
VattenfallVattenfall opines
that this technology is considered not to be a final solution for CO2
reduction in the atmosphere, but provides an achievable solution in
the near term while more desirable alternative solutions to power
generation can be made economically practical.[133] In 2014 research
and development were discontinued due to high costs making the
technology unviable.[134]
Bioremediation
The white rot fungus
Trametes versicolorTrametes versicolor can grow on and metabolize
naturally occurring coal.[135] The bacteria
Diplococcus has been found
to degrade coal, raising its temperature.[136]
Economic aspects
CoalCoal (by liquefaction technology) is one of the backstop resources
that could limit escalation of oil prices and mitigate the effects of
transportation energy shortage that will occur under peak oil. This is
contingent on liquefaction production capacity becoming large enough
to satiate the very large and growing demand for petroleum. Estimates
of the cost of producing liquid fuels from coal suggest that domestic
U.S. production of fuel from coal becomes cost-competitive with oil
priced at around $35 per barrel,[137] with the $35 being the
break-even cost. With oil prices as low as around $40 per barrel in
the U.S. as of December 2008, liquid coal lost some of its economic
allure in the U.S., but will probably be re-vitalized, similar to oil
sand projects, with an oil price around $70 per barrel.
In China, due to an increasing need for liquid energy in the
transportation sector, coal liquefaction projects were given high
priority even during periods of oil prices below $40 per barrel.[138]
This is probably because
ChinaChina prefers not to be dependent on foreign
oil, instead utilizing its enormous domestic coal reserves. As oil
prices were increasing during the first half of 2009, the coal
liquefaction projects in
ChinaChina were again boosted, and these projects
are profitable with an oil barrel price of $40.[139]
ChinaChina is the largest producer of coal in the world. It is the world's
largest energy consumer, and relies on coal to supply 69% of its
energy needs.[140] An estimated 5 million people worked in China's
coal-mining industry in 2007.[141]
CoalCoal pollution costs the EU €43 billion each year.[142] Measures to
cut air pollution may have beneficial long-term economic impacts for
individuals.[143]
Energy densityEnergy density and carbon impact
See also:
EnergyEnergy value of coal
The energy density of coal, i.e. its heating value, is roughly 24
megajoules per kilogram[144] (approximately 6.7 kilowatt-hours per
kg). For a coal power plant with a 40% efficiency, it takes an
estimated 325 kg (717 lb) of coal to power a 100 W
lightbulb for one year.[145]
As of 2006, the average efficiency of electricity-generating power
stations was 31%; in 2002, coal represented about 23% of total global
energy supply, an equivalent of 3.4 billion tonnes of coal, of which
2.8 billion tonnes were used for electricity generation.[146]
The US
EnergyEnergy Information Agency's 1999 report on CO2 emissions for
energy generation quotes an emission factor of 0.963 kg CO2/kWh
for coal power, compared to 0.881 kg CO2/kWh (oil), or
0.569 kg CO2/kWh (natural gas).[147]
Underground fires
Main article:
Coal seamCoal seam fire
Thousands of coal fires are burning around the world.[148] Those
burning underground can be difficult to locate and many cannot be
extinguished. Fires can cause the ground above to subside, their
combustion gases are dangerous to life, and breaking out to the
surface can initiate surface wildfires.
CoalCoal seams can be set on fire
by spontaneous combustion or contact with a mine fire or surface fire.
Lightning strikes are an important source of ignition. The coal
continues to burn slowly back into the seam until oxygen (air) can no
longer reach the flame front. A grass fire in a coal area can set
dozens of coal seams on fire.[149][150]
CoalCoal fires in
ChinaChina burn an
estimated 120 million tons of coal a year, emitting 360 million metric
tons of CO2, amounting to 2–3% of the annual worldwide production of
CO2 from fossil fuels.[151][152] In
Centralia, PennsylvaniaCentralia, Pennsylvania (a borough
located in the
Coal RegionCoal Region of the United States), an exposed vein of
anthracite ignited in 1962 due to a trash fire in the borough
landfill, located in an abandoned anthracite strip mine pit. Attempts
to extinguish the fire were unsuccessful, and it continues to burn
underground to this day. The Australian
Burning MountainBurning Mountain was
originally believed to be a volcano, but the smoke and ash come from a
coal fire that has been burning for some 6,000 years.[153]
At Kuh i Malik in Yagnob Valley, Tajikistan, coal deposits have been
burning for thousands of years, creating vast underground labyrinths
full of unique minerals, some of them very beautiful. Local people
once used this method[clarification needed] to mine ammoniac. This
place has been well-known since the time of Herodotus, but European
geographers misinterpreted the Ancient Greek descriptions as the
evidence of active volcanism in
TurkestanTurkestan (up to the 19th century,
when the Russian army invaded the area).[citation needed]
The reddish siltstone rock that caps many ridges and buttes in the
Powder River BasinPowder River Basin in
WyomingWyoming and in western
North DakotaNorth Dakota is called
porcelanite, which resembles the coal burning waste "clinker" or
volcanic "scoria".[154] Clinker is rock that has been fused by the
natural burning of coal. In the
Powder River BasinPowder River Basin approximately 27 to
54 billion tons of coal burned within the past three million
years.[155] Wild coal fires in the area were reported by the Lewis and
Clark Expedition as well as explorers and settlers in the area.[156]
Market trends
In 2006,
ChinaChina was the top producer of coal with 38% share followed by
the
United StatesUnited States and India, according to the British Geological
Survey. As of 2012 coal production in the
United StatesUnited States was falling at
the rate of 7% annually[157] with many power plants using coal shut
down or converted to natural gas; however, some of the reduced
domestic demand was taken up by increased exports[158] with five coal
export terminals being proposed in the
Pacific NorthwestPacific Northwest to export
coal from the
Powder River BasinPowder River Basin to
ChinaChina and other Asian
markets;[159] however, as of 2013, environmental opposition was
increasing.[160] High-sulfur coal mined in Illinois which was
unsaleable in the
United StatesUnited States found a ready market in Asia as
exports reached 13 million tons in 2012.[161]

WorldWorld coal reserves
The 948 billion short tons of recoverable coal reserves estimated by
the
Energy Information AdministrationEnergy Information Administration are equal to about 4,196 BBOE
(billion barrels of oil equivalent).[39] The amount of coal burned
during 2007 was estimated at 7.075 billion short tons, or 133.179
quadrillion BTUs.[162] This is an average of 18.8 million BTU per
short ton. In terms of heat content, this is about 57,000,000 barrels
(9,100,000 m3) of oil equivalent per day. By comparison in 2007,
natural gas provided 51,000,000 barrels (8,100,000 m3) of oil
equivalent per day, while oil provided 85,800,000 barrels
(13,640,000 m3) per day.
British Petroleum, in its 2007 report, estimated at 2006 end that
there were 147 years reserves-to-production ratio based on proven coal
reserves worldwide. This figure only includes reserves classified as
"proven"; exploration drilling programs by mining companies,
particularly in under-explored areas, are continually providing new
reserves. In many cases, companies are aware of coal deposits that
have not been sufficiently drilled to qualify as "proven". However,
some nations haven't updated their information and assume reserves
remain at the same levels even with withdrawals.
Of the three fossil fuels, coal has the most widely distributed
reserves; coal is mined in over 100 countries, and on all continents
except Antarctica. The largest reserves are found in the United
States, Russia, China,
AustraliaAustralia and India. Note the table below.

Major coal producers
See also: List of countries by coal production
The reserve life is an estimate based only on current production
levels and proved reserves level for the countries shown, and makes no
assumptions of future production or even current production trends.
Countries with annual production higher than 100 million tonnes are
shown. For comparison, data for the
European UnionEuropean Union is also shown.
Shares are based on data expressed in tonnes oil equivalent.

Major coal consumers
Countries with annual consumption higher than 100 million tonnes are
shown. For comparison, data for the
European UnionEuropean Union is also shown.
Shares are based on data expressed in tonnes oil equivalent.

Major coal exporters
Countries with annual gross export higher than 10 million tonnes are
shown. In terms of net export the largest exporters are still
AustraliaAustralia (328.1 millions tonnes),
IndonesiaIndonesia (316.2) and Russia
(100.2).

Exports of
CoalCoal by Country and year (million short tons)[5][167][168]

Major coal importers
Countries with annual gross import higher than 20 million tonnes are
shown. In terms of net import the largest importers are still Japan
(206.0 millions tonnes),
ChinaChina (172.4) and
South KoreaSouth Korea (125.8).[169]

Cultural usage
CoalCoal is the official state mineral of Kentucky.[170] and the official
state rock of Utah;[171] both U.S. states have a historic link to coal
mining.
Some cultures hold that children who misbehave will receive only a
lump of coal from
Santa ClausSanta Claus for Christmas in their christmas
stockings instead of presents.
It is also customary and considered lucky in Scotland and the North of
EnglandEngland to give coal as a gift on New Year's Day. This occurs as part
of First-Footing and represents warmth for the year to come.
See also